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  Java Practices -> Do not break portability
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<div class='page-title'>Do not break portability</div>

<div class='main-body'>
 
<br>Portability is one of the principal advantages of using Java.
<p>Sun Microsystems has published these <a href="http://java.sun.com/products/archive/100percent/4.1.1/index.html">guidelines</a>
for ensuring that a Java application remains portable.
<p>Highlights of these guidelines include :
<ul>
<li>
do not use hard coded file names and paths - use the <tt>File</tt> class,
and allow file paths to be configured during deployment.</li>

<li>
remember that some systems have case sensitive file names (Unix), while
others do not (Windows)</li>

<li>
be very wary of <tt><a href="http://java.sun.com/javase/6/docs/api/java/lang/Runtime.html">Runtime</a>.exec</tt>
and <tt>Method.<a href="http://java.sun.com/javase/6/docs/api/java/lang/reflect/Method.html#invoke(java.lang.Object, java.lang.Object...)">invoke</a></tt></li>

<li>
do not rely on thread scheduling and <a href='TopicAction8b10-2.html'>thread priorities</a> to define program logic</li>

<li>
do not use <tt>native</tt> methods</li>

<li>
do not hard code sizes and positions of GUI elements - use a <tt><a href="http://java.sun.com/javase/6/docs/api/java/awt/LayoutManager.html">LayoutManager</a></tt>
instead</li>

<li>
do not rely on a specific screen resolution - use <tt>java.awt.Toolkit.<a href="http://java.sun.com/javase/6/docs/api/java/awt/Toolkit.html#getScreenResolution()">getScreenResolution</a></tt>
instead</li>

<li>
do not hard code colors using numeric values - use the symbolic constants
in <tt>java.awt.<a href="http://java.sun.com/javase/6/docs/api/java/awt/Color.html">Color</a></tt>
and <tt>java.awt.<a href="http://java.sun.com/javase/6/docs/api/java/awt/SystemColor.html">SystemColor</a></tt>
instead</li>

<li>
do not hard code text sizes</li>

<li>
use the <tt>System.<a href="http://java.sun.com/javase/6/docs/api/java/lang/System.html#getProperty(java.lang.String)">getProperty(String)</a></tt>
method to refer to items which depend on the system, such as line terminators and path separators
</li>

</ul>

<p>Common <tt>System.getProperty(String)</tt> items can be placed in a general purpose 
<a href='TopicAction03b1-2.html'>constants class</a> :
<br>
<PRE>

<span class='comment'>/**
* Collected constants of very general utility.
*
* All constants must be immutable.
* No instances of this class can be constructed.
*/</span>
<span class='keyword'>public</span> <span class='keyword'>final</span> <span class='keyword'>class</span> Consts {

  <span class='comment'>/**
  * Prevent object construction outside of this class.
  */</span>
  <span class='keyword'>private</span> Consts(){
    <span class='comment'>//empty
</span>  }

  <span class='comment'>/**
  * Only refer to primitives and immutable objects.
  *
  * Arrays present a problem since arrays are always mutable.
  * DO NOT USE public static final array fields.
  * One style is to instead use an unmodifiable List, built in a
  * static initializer block.
  *
  * Another style is to use a private array and wrap it up like so:
  * &lt;pre&gt;
  *  private static final Vehicle[] PRIVATE_VEHICLES = {...};
  *  public static final List VEHICLES =
  *         Collections.unmodifiableList(Arrays.asList(PRIVATE_VEHICLES));
  * &lt;/pre&gt;
  */</span>

  <span class='comment'>//characters
</span>  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String NEW_LINE = System.getProperty(<span class='literal'>"line.separator"</span>);
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String FILE_SEPARATOR = System.getProperty(<span class='literal'>"file.separator"</span>);
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String PATH_SEPARATOR = System.getProperty(<span class='literal'>"path.separator"</span>);

  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String EMPTY_STRING = <span class='literal'>""</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String SPACE = <span class='literal'>" "</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String PERIOD = <span class='literal'>"."</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String TAB = <span class='literal'>"&#092;t"</span>;

  <span class='comment'>//algebraic signs
</span>  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> <span class='keyword'>int</span> POSITIVE = <span class='literal'>1</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> <span class='keyword'>int</span> NEGATIVE = -<span class='literal'>1</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String PLUS_SIGN = <span class='literal'>"+"</span>;
  <span class='keyword'>public</span> <span class='keyword'>static</span> <span class='keyword'>final</span> String NEGATIVE_SIGN = <span class='literal'>"-"</span>;
} 
</PRE>
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction03b1-2.html?Id=2'>Class for constants</a> <br>
 
  
  <a href='TopicAction8b10-2.html?Id=53'>Thread priorities are not portable</a> <br>
 
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